A 670 nm external-cavity single mode diode laser continuously tunable over 18 GHz range

It is demonstrated that a 670 nm visible diode laser, operating in external cavity and without any additional anti-reflection coating treatment on the output facet, can perfectly operate in a single mode regime and can be continuously tuned over a frequency range larger than 18 GHz. The external cavity is closed by a grating and it does not need etalons or other frequency selective devices. The very wide single mode scanning has been obtained by a servo system which locks the internal laser solitary cavity to the external one that is supported by three quartz bars. An example of a linear single frequency scanning is reported where the absorption spectrum corresponding to the 2S --> 2P transition of Li-7 is shown.